This disclosure relates to counting and integrating pixels, detectors, and methods of using the same.
X-ray imaging systems include an x-ray source and a detector. A specimen is placed between the source and the detector. The detector may directly or indirectly detect incident x-ray photons. Two main categories of detectors are current integrating detectors (CID) or energy integrating detectors (EID) and photon counting detectors (PCD). Some x-ray PCDs rely on continuous time current monitoring and pulse counting implementation of photon counting. Each pixel typically contains a pulse shaping circuit along with a thresholding system connected to a counter. This either dramatically reduces the fill factor of the pixel or necessitates the use of overlaid photodiodes using exotic materials like cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe or CZT). The resolution of the system is also limited by the need to accommodate all the circuitry.
When complementary metal-oxide-semiconductor (CMOS) photodiodes are used for photon counting, a continuous time current pulse monitoring approach is used. The pixel in such a system requires a large amount of circuitry to achieve photon counting. This limits the fill factor of a pixel and thus the counting capability of the pixel. In addition, the spectral capabilities of the sensor are limited by the available space, as the circuitry for each additional energy bin is placed in the pixel.